1. Field of the Invention
This invention relates to a process for the separation and purification of crude vinylphenol, and more specifically, to a process for the separation and purification of crude vinylphenol using an extracting procedure employing an aqueous alkali solution as an extracting agent with a specific organic solvent. For brevity, this extracting procedure will be referred to hereinafter as "an alkali extracting procedure" or simply as "an extracting procedure".
2. Description of the Prior Art
A number of methods for producing vinylphenol have been proposed and studied. These methods include, for example, a method involving recovering vinylphenol from a natural product, a method in which hydroxycinnamic acid is decomposed, a method wherein bis-(hydroxyphenyl) ethane is decomposed, a method in which ethylphenol is dehydrogenated, a method wherein o-coumaric acid is decomposed, and a method which comprises synthesizing acetoxystyrene from phenol and saponifying the acetoxystyrene. In all of these methods, the product obtained is crude vinylphenol containing vinylphenol and impurities such as hydrocarbons, alkylphenols, vinylphenol polymer and other phenols. For example, the product obtained by decomposing hydroxycinnamic acid contains impurities such as about 0 to 50% by weight of phenol, about 0 to 30% by weight of ethylphenol, about 0 to 5% by weight of vinylphenol polymer and about 0 to 105 by weight of unreacted hydroxycinnamic acid in addition to the vinylphenol. The product obtained by decomposing bis-(hydroxyphenyl) ethane contains about 0 to 50% by weight of phenol, about 0 to 20% by weight of ethylphenol and about 0 to 5% by weight of vinylphenol polymer. The product obtained by dehydrogenating ethylphenol contains about 0 to 10% by weight of phenol, about 0 to 90% by weight of ethylphenol, about 0 to 5% by weight of cresol, and about 0 to 5% by weight of vinylphenol polymer. The product obtained by decomposing o-coumaric acid contains about 0 to 10% by weight of phenol, about 0 to 30% by weight of ethylphenol, about 0 to 5% by weight of vinylphenol polymer, and about 0 to 10% by weight of unreacted o-coumaric acid. The product obtained by saponifying acetoxystyrene synthesized from phenol contains about 0 to 10% by weight of phenol, about 0 to 50% by weight of ethylphenol, and about 0 to 5% by weight of vinylphenol polymer. Therefore, purification of the crude vinylphenol so produced is essential.
To date, only one method has been reported for separating and purifying vinylphenol, which is a laboratory-scale purification of vinylphenol by recrystallization (B.B. Corson et. al.; J. Org. Chem. 23 548, 1958) However, poor separation and yields are obtained using this method and, hence, this method is not commercially feasible. Until now there has been no proposal of a method of separating and purifying vinylphenol which can be performed on a commercial scale with good efficiency.